1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image by an image forming unit on a sheet by transporting the sheet held in a main body sheet feeding tray, and particularly to an image forming apparatus capable of expanding an optional sheet feeding device on the lower side of the main body sheet feeding tray, and the optional sheet feeding device.
2. Description of the Related Art
Conventionally, an image forming apparatus including an image forming apparatus main body that has an image forming unit for forming an image on a sheet, a detachable main body sheet feeding tray for holding the sheet and a sheet feeding unit for feeding the sheet from the main body sheet feeding tray toward the image forming unit, and an optional sheet feeding device that can be added on the lower side of the main body sheet feeding tray and feeds the sheet toward the image forming unit has been proposed. A portion of the main body sheet feeding tray constitutes a portion of a transport path of the sheet which extends from the optional sheet feeding device to the image forming unit when the main body sheet feeding tray is attached to a proper position (for example, see JP-A-11-310328).
In this kind of image forming apparatus, when the main body sheet feeding tray is attached to the proper position of the image forming apparatus main body, the sheet held in the main body sheet feeding tray can be transported toward the image forming unit by the sheet feeding unit to form an image by the image forming unit on the sheet. Also, when the main body sheet feeding tray is attached to the proper position and the optional sheet feeding device is added on the lower side of the main body sheet feeding tray, the portion of the main body sheet feeding tray constitutes the portion of a transport path of the sheet which extends from the optional sheet feeding device to the image forming unit. Therefore, the sheet can also be fed from the optional sheet feeding device toward the image forming unit through the portion of the main body sheet feeding tray to form an image on the sheet.